This invention relates to vapor generation, and more specifically to generation of steam from contaminated feedwater, which steam can be used for recovery of sub-surface heavy oil and the like.
Steam injection is used for extraction of heavy oil and bitumin from deep deposits. In order to minimize costs, the water to be heated in a vapor generator to produce the steam for this injection is often taken from conveniently located surface sources of water, such as ponds and lakes, or is water recovered from underground with the oil or bitumin extracted from the deposits. The water taken from these sources is usually contaminated with salts or other solids which can accumulate as deposits or scale on inside walls of generator components as the water is heated while flowing through the vapor generator. Consequently, the vapor generator must frequently be shut down for cleaning, in order to avoid overheating and resultant failure of components upon which deposits have formed. This is especially true of tubular heat exchange elements disposed in high heat flux locations of the vapor generator. Although it is possible to treat the water before heating it, such treatment is relatively expensive and is thus limited to the minimum amount possible.
The present invention provides a vapor generator with an octagonal cross-section furnace characterized by a relatively large volume and moderate heat flux. The vapor generator includes evaporator surface located in a relatively low heat flux portion of the vapor generator. The vapor generator lends itself to in-shop fabrication, and because of the disposition of the final evaporaton surface in a low heat-flux location, the likelihood of scale formation is lessened and thus the period of operation between necessary cleanings is lengthened.